Image resizing Loss of Quality

[Oval]

On 2. März 2016 at 8:11 PM, JimmyJack said:

Oval.... here's a better example(s).

Lanczos sep, non sep.

Thanks! Sorry, they do not answer the question. What do those new examples demonstrate? I get much better results. About 4 times better! Have you done it in AP? There must be a big fault … if you have done the right steps then we would think that different hardware result in different results.

[JimmyJack]

Thanks! Sorry, they do not answer the question. What do those examples demonstrate?

 

Lol. I'm just throwing up an example of the exact pixel size down-sample in question. 

A reduction that's giving a "horrible" result. We really don't know what that means...

It's simply there for comparison sake, for the OP to say "I'm getting much worse than that".... or not.

[Oval]

It's simply there for comparison sake, for the OP to say "I'm getting much worse than that".... or not.

 

But why do you get those results? I get much better results in AP. About 4 times better! Have you done it in AP? There must be a big fault …

 

upper your, lower mine with AP

 

This is not funny! What have you done? Please tell us that you are working for Adobe.  ;) 

[JimmyJack]

Uh..... what are you doing?

What is your process?

 

Do you see the size difference between my two images?

[Oval]

On 2. März 2016 at 10:11 PM, JimmyJack said:

Uh..... what are you doing?

What is your process?

 

Do you see the size difference between my two images?

 

I have two eyes! Questions do not answer the question why you get worser results. Why? I only have two possible explications.

[JimmyJack]

why are u so angry? We are all on the same team here.

 

I'm asking because I suspect we are at crossed signals....seeing two different problems here.

 

I've told you my process: I went from one pixel size to another, at the same dpi, with a certain resample method in AP.

The result is an image that is much much much smaller on screen at pixel resolution than the original.

At pixel res, I took a screen shot of both.

 

The image you are showing me as mine bares no resemblance to what Im seeing on my screen.

It's seems as though you are zoomed in.

 

And... if you're getting much better results I would love to know how!

Can you please tell me what you did to get there?

 

Could this be the difference between a Retina screen capture and non retina resolution? 144 vs 72?

 

Edit: I've put the resized image on the original and did an export instead of a grab.

I think you will like this one.  :)

[Oval]

why are u so angry? We are all on the same team here.

 

No, not angry! You showed bad pictures @ 100% that do not show the great results that you normally achieve with AP. That damages the image of the software. Here is the comparison:

 

 

“The image you are showing me as mine bares no resemblance to what Im seeing on my screen. It's seems as though you are zoomed in.”

 

No! Rubbish! Everything @ 100%, normal export with AP.

[JimmyJack]

So please, I'm begging you, tell me what I'm doing wrong.

 

This could very well be the point and solution for this entire thread!!

 

Is this better.....

[Oval]

So please, I'm begging you, tell me what I'm doing wrong.

…

Is this better.....

Great! We don’t know if you make something wrong (we do not think so) but the first pictures did not show the quality of AP. Of course that new picture is much better in comparison.  :) But it does not explain why timur and the teacher (think they) get bad results. We don’t know details of their workflow and the pictures, so we only can tell them: No, we never ever had bad results! We trust in Serif and hope Serif will tell us with pictures why timur and accendare thought they got bad results. 

[R C-R]

If I understand correctly, when you cram a large number of pixels into a smaller area than its original area, the detail and resolution increases (and in the opposite case, decreases). Is that correct?

No, there is no change in the detail or the image's resolution. Pixels don't actually get closer to each other or farther apart. When you print the ink or toner dots (or equivalent in other printing methods) do, but dots & pixels are not the same thing. Also note that some print setting will override the file's dpi settings, like if in the OS X print dialog you change the scale, print two up to a page, change margin settings, etc.

 

DPI also is irrelevant for setting display size on web pages. The HTML <img> tag usually defines the default display width & height dimensions, but again there are things that will override that. For example, if you are viewing this page with Safari on OS X, tapping the plus or minus keys with the Command key held down will change the zoom level, as will the "pinch" gesture if you are viewing the page on an iPhone or iPad.

 

Web pages are not like printed documents. They are really just a set of instructions a browser's layout engine (like WebKit or Gecko) uses to assemble various elements from various sources into a viewable page. Depending on the engine, window size, platform, OS, & several other factors they may be assembled in different ways that look quite different from each other. An extreme example of this is Safari's Reader View mode. If you are viewing this page with a recent version of Safari, you should see a four line icon in the URL window at the top of the page. Hover the mouse pointer over it & note that the URL changes to "Show Reader View." Click on that & you will see a very different version of this page.

[R C-R]

Mmmm, it's an exaggerated view of what it looks like at pixel level. Pixel level is pixel level.

But without context, "pixel level" can mean any of several different things. A bitmapped image has an inherent pixel resolution, but so does a screen display. They are not the same thing, nor is the "pixel level" at which a browser, Affinity, or other apps can display an image. A bitmapped image's pixel resolution is the only "pixel level" that remains the same in all contexts.

[deborah]

Thanks for all the info -- it gives me lots to think about as it is changing my whole understanding of pixels, dots, resolution, etc. When I said printing I'm talking about through a print house where our images have to be high quality 340 to 350 dpi for the books we publish.

 

Now that I'm using AP rather than Photoshop, I feel like I'm back in kindergarten! 

[Oval]

our images have to be high quality 340 to 350 dpi for the books we publish.

 

Depends on the raster. If you have high contrast pictures you even need more pixels (>400dpi @ 100%).

 

kindergarten … no, you are kidding!

[TatianKa]

Hello everyone, I think I found a solution!!! It is not the image you need to work with. Go to Preferences > Performance > View quality and make sure it is set to Bilinear and not the Nearest Neighbor. Then when you resize the image Affinity keeps the quality and during export it looks perfect as well :) The advice is originally by Gear maker from another line, thanks to him! :)

[Fixx]

Are you saying Preferences > Performance > View quality affects not only to view quality but also to actual destructive pixel editing?

If so: OK, but really this should be known and understood by users. 

[Oval]

Hello everyone, I think I found a solution!!! It is not the image you need to work with. Go to Preferences > Performance > View quality and make sure it is set to Bilinear and not the Nearest Neighbor. Then when you resize the image Affinity keeps the quality and during export it looks perfect as well :) The advice is originally by Gear maker from another line, thanks to him! :)

 

View Quality influences the view quality, not the export quality. What was discussed was the export quality.

[TatianKa]

View Quality influences the view quality, not the export quality. What was discussed was the export quality.

I understand, I just thought that many might not know about this option in preferences :)

[Oval]

I understand, I just thought that many might not know about this option in preferences :)

 

This was just to avoid misunderstandings. You wrote “I think I found a solution!!!”, but this is not a solution to get better export results or to explain "poor” export.  :wub:

[TatianKa]

This was just to avoid misunderstandings. You wrote “I think I found a solution!!!”, but this is not a solution to get better export results or to explain "poor” export.

Yes, you are right, Oval :)

[Fixx]

Why this arises is maybe because we are not talking about export quality, but resizing quality, or rather any transformation which may be needed to be rasterized before it can be used as part of work flow. All is fine is you let export do all resampling but there are no controls or even any knowledge what resampling method happens when you select "rasterize".

[R C-R]

Are you saying Preferences > Performance > View quality affects not only to view quality but also to actual destructive pixel editing?

I am fairly sure that is not true. View quality only affects how the document is rendered on the screen. It determines what method is used to map image pixels to screen pixels when they are not the same. Nearest Neighbor is less computationally intensive than Bilinear & therefore renders faster, but is usually less accurate.

 

The tl;dr version: Resizing/resampling can seem confusing but one thing that might help is to keep in mind that a digital graphics file is just an abstraction that has to be rendered to be seen. Rendering it to a computer screen at some display size with a graphics app does not determine how it will be rendered when printed or when viewed in a web browser, an email client app, or whatever.

 

With the exception of plotters, the rendered output will be a rasterized (bitmapped) image composed of pixels, which are the smallest "picture elements" the output device can divide the image into. Since there is almost never an exact, 1:1 match between these picture elements (however they are defined in their abstracted digital representation) & how the output device can render them, some form of interpolated mapping must be used, like nearest neighbor or bilinear resampling, if they are to resemble their elemental form with acceptable accuracy.

 

The short version: rasterized images are composed of pixels. The number of pixels they contain determines how much detail they can contain. If you reduce that number, you reduce their capacity to retain detail, accuracy, or quality. There is no workaround for this; the best you can do is to avoid trying to include more detail than that number of pixels can show.

[Fixx]

R C-R, I am not sure what you trying to say with that resolution basics.

 

Probably this whole discussion had nothing to do about rasterizing scaled images; which is still a grey area in AP mechanism.  :rolleyes:

[Oval]

Why this arises is maybe because we are not talking about export quality

 

It is about export quality: timur needed a file for a website: “I have tried exporting the image and tried all the options on the pop-up box (yes including lanczos).”

“the pictures is 5847x2535”

“I am trying to get it to 959x (whatever the equivalent of that is)”

“The picture is degraded so bad that I don't want to post it on the website anymore.”

“I have full width of screen picture on the website and on the backend it is requesting me to input 950 pixel wide picture which is not the actual size needed.”

Even accendare needed a web ready file.

[Oval]

Probably this whole discussion had nothing to do about rasterizing scaled images; which is still a grey area in AP mechanism.  :rolleyes:

 

If you want to know details of the mechanism/algorithms, you could start a new topic.

[Fixx]

I asked it once and got answered "it might be nearest neighbor".